A motor vehicle electric power steering generally comprises an electromechanical actuator situated on the steering column or on the lower assembly which comprises mechanical components intended to perform the angular positioning of the steered wheels of the vehicle. The electromechanical actuator comprises a rotary electric motor the shaft of which is supported by at least one rolling bearing, either directly or via a ball-screw system.
The rolling bearing generally comprises an inner ring, an outer ring and a row of rolling elements, generally balls, arranged in between the rings.
A retaining cage for a rolling bearing comprising a plurality of pockets for housing balls each of which is defined in part by two claws arranged on the opposite side to a heel of the said cage is known from document FR-A1-2 911 934. Such cages are completely satisfactory in a great many applications. However, in applications involving a low rotational speed, or in applications in which the direction of rotation reverses sharply, this kind of cage runs into various difficulties. Specifically, under the effect of the balls, the cage may suffer extensive deformation and come into contact with the inner ring, causing it to become damaged or even destroyed.
In addition, when the direction in which the load is applied to the bearing is changed, for example when the wheels of a vehicle equipped with an electric power steering as described hereinabove are turned as the driver manoeuvres to the left and to the right when parking the vehicle, the cage is likewise severely deformed, or even destroyed. Moreover, it may also prove difficult to fit such a cage over the balls.
A cage comprising pockets of ellipsoidal shape, defined in such a way that each rolling element present in a corresponding pocket is in contact via the bottom of the pocket and via the two means of axial retention of the cage on the corresponding rolling element is also known, from document JP 2001-355637. A space remains between the rolling element and the side walls of the pocket in order to form a reservoir for lubricant.
However, because each rolling element is held in the corresponding pocket by three points of contact, the rolling elements cannot move circumferentially in relation to the corresponding pocket.
The rolling elements are therefore unable to move relative to one another, and this generates a significant risk of deformation if two adjacent rolling elements attempt to move in opposing directions.
The present invention seeks to overcome these disadvantages.